Shibendra Shekher Sikder, Department of Physics, Khulna University of Engineering and Technology (KUET) for his indispensable guidance, great interest, constructive suggestions, fruitful discussion and constant inspiration during the research work. Head, Department of Physics, Khulna University of Engineering & Technology, who has supported me greatly in various ways throughout the period of my studies in this department.
Contents
Temperature 115 5.5 Specific magnetization measurement of nanocrystalline amorphous ribbons 117 5.5.1 Effect of annealing temperature on specific magnetization at room.
CHAPTER- V
Fig.-5.1 l(a. b) Frequency dependence of imaginary part of complex permeability of 108 (Feo 95Coo 05)73.sCu 1Nb3Si13.5B9 alloy at different annealing temperatures. Fig.-5.13(a, b) Temperature dependent real part of initial complex permeability of 113 (Feo95Co0.05) 73.5Cui Nb3Si135B9 alloy at different annealing temperatures. for a continuous baking time of 30 minutes.
- Introduction
- The Aim and Objectives of the Present Work
- Experimental reason for Choosing this Research Work
- Organization of the Thesis
- Composition of the Nanocrystalline
- An Overview of Nanocrystalline Materials
- Alloy Design Issues
- Stages of Evolution of Microstructure
- Advantages of Soft Nanocrystalline Alloys
Impact of microstructural control on the development of state-of-the-art soft magnetic materials. The crystallization behavior of this x = 0 alloy is quite different and leads to a severe deterioration of the soft magnetic properties compared to the original.
FINEMET
- Viscosity condition for the Formation of Metallic glass
- Methods used for Preparation of Nanocrystalline Alloy
- The Fast Cooling of the Melt
- Sample Preparation .1 Master alloy Preparation
- Preparation of ribbon by Melt Spinning Technique
- Important Factors to Control the Thickness of Ribbons
- Confirmation of Amorphousity of Ribbon
In this thesis, amorphous ribbons were fabricated by rapid cooling of the melt. The temperature was monitored by an external pyrometer from the top surface of the molten alloy.
Chapter-Ill Theoretical Background
Amorphous Alloy or Metallic Glass
- Nature and Formation of Amorphous Alloys
- Factors Contributing to Glass Formation and Stability
Near the glass transition temperature (Tg) atomic motion is completely suppressed and the amorphous structure rises inward, so that the onset time of crystallization. Melt viscosity, glass transition temperature (Tg) and homogeneous nucleation rate belong to the kinetic parameters.
Structure and Microstructure of Amorphous and Nanocrystalline alloys
Since the formation of an amorphous alloy depends on the absence of long-range order, change of composition is expected to effect Tg and T. The pair correlation function is defined as the probability that two atoms in the structure are separated by a distance. Two additional atomic distribution functions related to the pair correlation function are the spatially dependent atomic density, p(r), which is defined as.
On the other hand, a crystalline solid has a set of discrete distances between atomic positions and thus the pair correlation function in a set of discrete s-like functions, the amplitude of which reflects the particular nearest-neighbor coordination number. .etc.
Stability of the Amorphous Nanocrystalline Materials
- Characteristics of the Glass Transition Temperature
The transition to the glassy state and the crystalline state is accompanied by an exothermic heating effect that gives rise to a sharp peak in the temperature dependence of the heat flow. Glass transition temperature (Tg) occurs when the time scale of molecular rearrangements is too long for equilibrium to be maintained. When the time scale of the experiment and the configurational relaxation time coincide, you start to see departure from equilibrium.
Operational definition of Tg is when the viscosity of the supercooled liquid exceeds 1013 NSm 2 .
Differential Thermal Analysis and its Application
- Eva'uation of Activation Energy Based on DTA Technique
Where, as in the liquid, there is an Arrenhiv's type with a Boltzmann factor containing an activation energy. Based on the work of Murray and White, the kinetics of crystallization of materials can be understood by interpreting the DTA patterns of the materials. The values of AE also appear to correlate well with the number of atomic species in the alloy; the more complex the alloy, the greater the AE.
From the measured data on the heating rate (/3) and the corresponding crystallization temperature (Ti), the activation energy can be deduced from the slope of the curve.
Determination of Nanometric Grain Size by X-ray Diffraction
Now consider the path differences for each of the two angles 0 and 0, for x-rays traveling through the full thickness of the crystal. The width P is usually measured in radians, an intensity equal to half the maximum intensity. As a rough measure of 3 we can take half the difference between the two extreme angles where the intensity is zero.
We now write path difference equations for these two angles, related to the entire thickness of the crystal rather than to the distance between adjacent faces.
Random Anisotropy Model (RAM)
To achieve such a reduction in coercivity, Herzer noted that the nanocrystalline grains must be exchange-coupled. The K,1 essentially determines the magnetic softness, since ft and the inverse of the initial permeability (hi) are proportional to K. Therefore, these quantities are expected to have a similar dependence on grain size and have been experimentally confirmed [3.28]. Herzer explained the grain size dependence of the ft based on RAM, where the nanocrystalline materials were considered as a single-phase magnetic system.
Since the dimensions of the crystallites dictate the unique properties, by controlling the annealing temperature of the samples, the magnetic softness or hardness is determined with respect to the permeability of the grain size.
Theories of Permeability
- Measurement of Initial Permeability
- Relative Permeability
- High Frequency Behavior and Losses
The presence of such a component requires a supply of energy to maintain the alternating magnetization, regardless of the origin of the delay. The initial permeability of a ferromagnetic substance is the combined effect of the wall permeability and rotational permeability mechanisms. Where L0 is the inductance of the winding coil without sample core and N is the number of the coil (here N=lO), S is the cross-sectional area as given below.
Where m = the weight of the tape, d and p are the mean diameter and density of the sample as follows.
Magnetic Dipole Moments and Magnetization
- Ferromagnetic ordering (Curie) Temperatures
- Hysteresis
At point "a" almost all the magnetic domains are aligned and an additional increase in the magnetizing force will result in a very small increase in the magnetic flux. The force required to remove residual magnetism from a material is called the coercive force (He) or coercivity of the material. Note that the curve has not returned to the origin of the graph because some force is required to remove the residual magnetism.
Retentivity: A measure of the residual flux density corresponding to the saturation induction of a magnetic material.
Thermal Analysis Techniques
- The Principle of Differential Thermal Analysis 1 40
- Apparatus
- Experimental Factors
- Interpretation and Presentation of DTA
And when the reaction is complete, the temperature of the sample gradually catches up with the temperature of the inactive sample. The area under the DTA peak can be related to the enthalpy change and is unaffected by the heat capacity of the sample. For porous, compacted, or stacked samples, the pore-filling gas can change the thermal conductivity of the atmosphere surrounding the DTA container and cause large errors in the peak region.
The situation worsens when gases evolve from the sample, making the thermal conductivity of the DTA cell environment different from that used in the calibration experiments.
Annealing
- Stages
- Setup and Equipment
The lightweight structure of the balance beam mechanism offers the following strengths: stability with respect to temperature fluctuations, reduction of buoyancy and a very sensitive balance, as well as the ability of the differential balance to cope with disturbances such as oscillation. There are three stages in the annealing process, the first being the recovery stage, which results in the softening of the metal by removing crystal defects (the primary type of which is the linear defect called dislocation) and the internal stresses they cause. . The interior of the oven is large enough to place the workpiece in a position that allows maximum exposure to the circulating heated air.
After the annealing process has been successfully completed, the workpieces are sometimes left in the oven so that the parts can undergo a controlled cooling process.
Thermal Treatment of the Amorphous Ribbon
Powder! Polycrystalline Diffraction
- Experimental Technique for X-ray diffractometer
- AnaLysis of XRD data
Usually, the lattice parameter of an alloy composition is determined by the Debye-Scherrer method after extrapolating the curve. The XRD pattern of (110) reflection for different stages of the heat treatment temperature of the alloy composition is used to calculate grain size. All values of grain size for each step of the heat treatment temperature of the alloy composition were determined.
In the amorphous matrix of the tape, crystalline nanograins were formed in the heat treatment process with Fe-Si composition.
Impedance Analyzer
- Preparation of the Samples for Complex Permeability Measurement
- Components of Complex Permeability Measurements
We made use of the excellent experimental facilities available at the Materials Science Division, Atomic Energy Centre, Dhaka. The sweep capabilities of the built-in frequency synthesizer and dc bias source allow fast and accurate measurements. It is therefore necessary to keep the capacitance of the winding as low as possible.
Here L is the inductance of the toroid and 1-0 is the inductance of the coil of the same geometric shape in vacuum.
Curie Temperature Measurements
- Inductance Analyzer
The temperature dependence of the initial permeability of the cast and annealed ribbons has been measured using a laboratory built oven and Wayne Kerr 3255 13. All of the above functions can be selected via manual control on the front panel or remotely via the GPIB interface for fully-automated high-speed testing. To measure the inductance of a component, the analyzer must be turned on with the test leads or fixture connected to the BNC connectors of the font panel.
The measurement can be performed as single short mode for single measurement or repeated mode for continuous measurement.
Magnetization Measurement Techniques
- Vibrating Sample Magnetometer (VSM)
- Principle of VSM
- Study of DTA Traces of (Feo.95Co0.05)73.5Cu1 Nb3Si 135B9 Alloy
- The Activation Energies for Formation of Nanocrystalline Phase
- A Comparison Between DTA Results of (Feo.95Co0.05)73.5Cu 1Nb3Si 135B9 Alloy and other FINEMET
- Identification of Phases by XRD Analysis
- Lattice Parameter Measurement
- Silicon Content in Nanograins
- Grain Size Determination
- Frequency Dependence of Initial Permeability of (Fe0.95Coo.05)73.5Cu1 Nb3Si13.5B9 Alloy with Different Annealing
- Frequency Dependence of Imaginary part of the Complex Permeability of (Feo.95Coo.05)73.5Cu 1Nb3Si 13•5B9 Alloy
- Relative Quality Factor
Understanding the onset of crystallization, the peak crystallization temperature, and the end of crystallization temperature is essential for determining the appropriate annealing temperature for nanocrystallization. In Figure 5.4, it is clear that at lower annealing temperature (550 °C) the FWHM of the peak is large and with the increase in annealing temperature the value of FWHM becomes smaller. The formation of the nanometric microstructure corresponding to grain growth with the increase of annealing temperature is attributed to the combined effects of Cu and Nb and their low solubility in iron.
The magnetic properties of soft magnetic materials are mainly determined by domain wall mobility, especially in the range of irreversible magnetization. Imaginary part of the complex permeability (p.11) at constant annealing time 30 minutes with different annealing temperature in the frequency range. The increase of the loss factor with the annealing temperature indicates that longer annealing time causes further growth of the crystallites and their stability.
Curie Temperature Measurement of Nanocrystalline Amorphous Ribbon of (Fe0.95Co0.05)73.5Cu N b3Si 13.5B9 Alloy
- The Variation of Curie Temperature with respect to Annealing Temperature
From the variation of pf with temperature for the toroidal samples annealed at 500 °C to 550 °C, the Curie temperature of the remaining amorphous matrix is determined from the maximum value of 418 °C, 402 °C and 272 °C for the sample annealed at 500 °C. °C. A likely reason for the decrease in Tc of the amorphous phase upon annealing above the crystallization temperature is that the amorphous matrix is iron-depleted and the relative amount of Nb in the amorphous matrix increases. An almost identical Curie temperature occurs when the sample is annealed in the range of 500 °C - 525 °C.
The likely reason for the decrease in the Curie temperature is that the amorphous matrix is iron-depleted and the relative amount of Nb in the amorphous matrix increases, which weakens the exchange interaction, resulting in a decrease in the Curie temperature of the amorphous matrix.
Specific Magnetization Measurement of NanocrystaHine Amorphous Ribbons
- Effect of Annealing Temperature on Specific Magnetization at Room Temperature
The present results are interpreted in terms of the conventional domain theory of ferromagnetism, where it is assumed that the effect of the annealing temperature is to partially remove the pinning centers of the domain wall and thereby improve the magnetic softness of this strip. Where the term was described as a direct consequence of the random anisotropy pattern and attributed to the FeCo(Si) grains. The coefficient a2 reflects the effective magnetic anisotropy predicted by Herzer of the nanocrystalline material, where as in the amorphous alloy it is postulated to be caused by local stress and magnetoelastic saturation magnetization of the junction 202.65emu1g observed at 600 °C.
Table-5.5 The values of saturation magnetization of (Feo9Co0 0)735Cu1 Nb3Si13 B9 alloy at different annealing temperature with constant annealing time 30 minutes.
Conclusions
The improvement in soft magnetic properties can be attributed to the highly refined grain structure in the range of 9 to 26 nm obtained at different annealing temperatures. Hacking; "Influence of annealing conditions on the nanocrystalline and ultrasoft magnetic characteristics of Fe755Cu,Nb1 Si135B9 alloy": J. Hono; "Optimization of microstructure and properties of co-substituted Fe-Si -B-Nb-Cu nanocrystalline soft magnetic alloys"; J.
Noor; "Effects of Two-Step Annealing on the Complex Permeability of Fe-Cu-Nb-Si-B Nanocrystalline Soft Magnetic Materials"; M.
